No. 516] THE CUTICULA OF CESTODES 



711 



but in many forms are connected with the cuticula by 

 branched or anastomosing processes (Figs. 1 and 2) which 

 are interpreted by many to be ducts. 



The lack of subcuticular cells in Aspidobothridae has 

 been shown by Monticelli (1892) and Nickerson (1902) 

 for Cotylogaster, Nickerson (1894) for Stichocotyle (Fig. 

 6), and Osborn (1904) for Cotylaspis. Single-celled 

 glands are, however, present in all these worms. 



In the other digenetic trematodes and in cestodes, also, 

 although subcuticular cells have been shown to be present 

 in most of the forms whose finer structure is known, it is 

 certain that some do not possess them. In Distomum 

 , palliatum and Distomum reticulatwm, for instance, Looss 

 (1885) found none of them, and in Hemiurus crenatus and 

 Gasterostomum gracilescens Lander (1904) and Tennent 

 (1906), respectively, found them only in very small num- 

 bers. In all digenetic trematodes and cestodes, also, it 

 can very often be shown that the cells in question bear 

 no adequate relation to the cuticula beneath which they 

 lie. Thus they are present sometimes in certain parts 

 of the body only, as has been shown in my study of 

 Apoblema (1898), in which the appendix of the youthful 

 distome, although covered with exactly the same cuticula 

 as in the rest of the body, is entirely without subcuticular 

 cells. The suckers, also, in cestodes and the tail of the 

 cercaria have none of these cells, although they possess 

 a cuticula. 



In many digenetic trematodes, too, the subcuticular 

 cells, although present, are entirely too few m number 

 to produce the thick cuticula present, as shown in Herni- 

 ary* crenatus (Fig. 7) by Lander, and in numerous other 

 cases. It must be remembered in this connection that the 

 cuticula of trematodes and cestodes is probably at all 

 times a growing tissue, which is constantly being renewed 

 on its inner surface in proportion as it wears away on its 

 outer, so that if the subcuticular cells are its matrix they 

 should be equally present in all parts of the body and at 

 all times of the animal 's active life. 



